I. Field of the Invention
The present invention relates to medical devices and methods generally aimed at spinal surgery. In particular, the disclosed system and associated method relate to performing spinal fusion.
II. Discussion of the Prior Art
Spinal discs serve to cushion and stabilize the spine in addition to distributing stress and damping cyclic loads. The discs may become damaged due to injury or age and symptoms of a damaged disc may include severe pain, numbness or muscle weakness. Fusion is one method of reducing the magnitude of the symptoms of damaged spinal discs. The primary goal of spinal fusion is to restore disc height and provide stability between adjacent vertebrae while promoting the formation of an osseous bridge between the adjacent vertebrae (so called “bony fusion”). Materials are often used in conjunction with the various stabilization devices to encourage bony fusion. Forming an osseous bridge requires osteogenic cells, an adequate blood supply, sufficient inflammatory response, preparation of the local bone to expose cancellous bone and a high quality graft material. The graft material must be conducive to the creeping substitution of bone and may be included within implants or used to construct the implants. Autograft and allograft bone are examples of materials conducive to natural bony fusion that are used to create bone implants.
Bone allograft implants have experienced proliferated use over time. A problem exists, however, in that cadaveric bone (used to produce bone allograft implants) is oftentimes of insufficient dimension to produce grafts of adequate height, especially in cervical applications. More specifically, the femur thickness (that is, the distance between the outer surface of the femur and the inner surface of the intermedullary canal) reduces with age. Therefore, as the donor pool ages, the thickness of donated femurs decreases. In the field of allograft processing, industry practice favors using this “femur thickness” dimension as the height of the resulting cervical allograft. However, the general reduction in the “femur thickness” dimension attributable to age effectively limits and creates a general shortage in the amount of cadaveric bone that can be used in such cervical applications because it is of insufficient dimension to restore disk height.
Efforts to overcome the size limitation have been undertaken (such as providing bone implants formed from multiple laminations), but have failed or are lacking in various respects. The shortcomings of the prior art coupled with the bone shortage have created the need for a system that is structurally improved while being adapted to the allograft bone that is available.
The present invention is directed at addressing this need and eliminating, or at least reducing, the effects of the shortcomings of the prior art systems as described above.